MCM-41- and HMS-type mesoporous silicas were found to be efficient catalysts for the continuous chemical fixation of CO(2) into 1,3-dimethyl-2-imidazolidinone with N,N'-dimethylethylenediamine in supercritical CO(2).
Dinitrogen-divanadium complexes with triamidoamine ligands, 1-3, were synthesized and characterized by resonance Raman, UV-vis, and NMR spectroscopy and elemental and X-ray structure analyses. X-ray structure analyses reveal that all three of the complexes have a dimeric structure with a μ-N ligand (N-N bond length 1.200-1.221 Å). Resonance Raman and NMR spectra of 1-3 in solution show that these complexes maintain a dimeric structure in benzene and toluene solutions. N NMR spectra of 1 and 3 have peaks assignable to μ-N ligands at 33.4 and 27.6 ppm, respectively, but 2 does not have a similar peak under the same conditions. In V NMR spectra, the peaks of vanadium ions were observed at -173.3, -143.8, and -240.2 ppm, respectively, which are in a higher magnetic field region in comparison to those of dinitrogen-divanadium complexes reported previously. The structure and electronic properties of 1 are supported by DFT calculations. Additionally, all complexes react with excess amounts of M[CH] (M = Na, K) and the proton sources HOTf, HCl, and [LutH]OTf (Lut = 2,6-dimethylpyridine) to produce ammonia without hydrazine. The ammonia produced was evaluated as an ammonium salt by H andN NMR spectroscopy. The yield of NH produced in the reaction of 1 with Na[CH] and HOTf under N was 151% (per V atom).
a-Tocopherol was synthesized using a condensation reaction of 2,3,6-trimethylhydroquinone with isophytol in supercritical CO 2 using batch and continuous-flow reactors. In the batch reaction catalyzed by a fluorinated molecular catalyst bearing strong Brønsted acidity, C 6 F 5 CHTf 2 (Tf ¼ SO 2 CF 3 ), an increase in the CO 2 pressure causes a marked increase in the product selectivity for a-tocopherol, albeit with a slight decrease in the product yield. The solubility measurements by extraction experiments and the supercritical fluid NMR (scNMR) indicate that the homogeneous and non-polar reaction phase in scCO 2 is crucial to obtain a-tocopherol with high selectivity. A continuous flow scCO 2 process for the condensation reaction can be performed with a strong acid resin, Amberlyst 15, as a solid acid catalyst to give the desired product with high selectivity.
We recently reported the syntheses, crystal structures, and protonation reactions of dinitrogen divanadium complexes bearing triamidoamine ligands, ([{V(LR)}2(µ‐N2)] (R = iBu (1), EtBu (2), and iPr2Bn (3)). In this study, we have additionally synthesized two novel dinitrogen‐divanadium complexes with similar derivatives (R = Bn (4) and MeBn (5)), which are characterized spectroscopically and structurally. The X‐ray structures have both revealed a divanadium complex with a bridging N2 ligand. The protonation reactions of the µ‐N2 ligands for 4 and 5 in the presence of M+[C10H8]– (M+ = Na+, K+) and proton source (HOTf or [LutH](OTf)) have given ammonia. Particularly, the NH3 yield from the reaction of 5 with K+[C10H8]– and [LutH](OTf) has been 341 %. Furthermore, mixed valence Na+ adduct of 1, [Na{V(LiBu)}2(µ‐N2)] (6), which is prepared by the reaction of 1 with sodium metal, has been prepared and its crystal structure has also been determined. Compound 6 is electrochemically and spectroscopically characterized, which is also evaluated by DFT calculation method.
A novel dinitrogen–dichromium complex, [{Cr(LBn
)}2(μ-N2)] (1), has been prepared from reaction of CrCl3 with
a lithiated
triamidoamine ligand (Li3LBn
) under
dinitrogen. The X-ray crystal structure analysis of 1 revealed that it is composed of two independent dimeric Cr complexes
bridged by N2 in the unit cell. The bridged N–N
bond lengths (1.188(4) and 1.185(7) Å) were longer than the free
dinitrogen molecule. The elongations of N–N bonds in 1 were also supported by the fact that the ν(N–N)
stretching vibration at 1772 cm–1 observed in toluene
is smaller than the free N2. Complex 1 was
identified to be a 5-coordinated high spin Cr(IV) complex by Cr K-edge
XANES measurement. The 1H NMR spectrum and temperature
dependent magnetic susceptibility of 1 indicated that
complex 1 is in the S = 1 ground state,
in which two Cr(IV) ions and unpaired electron spins of the bridging
N2
2– ligand are strongly antiferromagnetically
coupled. Reaction of complex 1 with 2.3 equiv of Na or
K gave chromium complexes with N2 between the Cr ion and
the respective alkali metal ion, [{CrNa(LBn
)(N2)(Et2O)}2] (2)
and [{CrK(LBn
)(N2)}4(Et2O)2] (3), respectively. Furthermore,
the complexes 2 and 3 reacted with 15-crown-5
and 18-crown-6 to form the respective crown-ether adducts, [CrNa(LBn
)(N2)(15-crown-5)] (4) and [CrK(LBn
)(N2)(18-crown-6)]
(5). The XANES measurements of complexes 2, 3, 4, and 5 revealed that
they are high spin Cr(IV) complexes like complex 1. All
complexes reacted with a reducing agent and a proton source to form
NH3 and/or N2H4. The yields of these
products in the presence of K+ were higher than those in
the presence of Na+. The electronic structures and binding
properties of 1, 2, 3, 4, and 5 were evaluated and discussed based on
their DFT calculations.
The reactions of newly designed lithiated triamidoamines Li3LR (R = iPr, Pen, and Cy2) with VCl3(THF)3 under N2 yielded dinitrogen–divanadium complexes with a μ-N2 between vanadium atoms [{V(LR)}2(μ-N2)] (R = iPr (1) and Pen (2)) for the former two, while not dinitrogen–divanadium complexes but a mononuclear vanadium complex with a vacant site, [V(LCy2)] (R = Cy2 (3)), were obtained for the third ligand. The V–NN2 and N–N distances were 1.7655(18) and 1.219(4) Å for 1 and 1.7935(14) and 1.226(3) Å for 2, respectively. The ν(14N–14N) stretching vibrations of 1 and 2, as measured using resonance Raman spectroscopy, were detected at 1436 and 1412 cm–1, respectively. Complex 3 reacted with potassium metal in the presence of 18-crown-6-ether under N2 to give a hetero-dinuclear vanadium complex with μ-N2 between vanadium and potassium, [VK(LCy2)(μ-N2)(18-crown-6)] (4). The N–N distance and ν(14N–14N) stretching for 4 were 1.152(3) Å and 1818 cm−1, respectively, suggesting that 4 is more activated than complexes 1 and 2. The complexes 1, 2, 3, and 4 reacted with HOTf and K[C10H8] to give NH3 and N2H4. The yields of NH3 and N2H4 (per V atom) were 47 and 11% for 1, 38 and 16% for 2, 77 and 7% for 3, and 80 and 5% for 4, respectively, and 3 and 4, which have a ligand LCy2, showed higher reactivity than 1 and 2.
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